I believe his point was that if you're going to call this unethical, then you have to also consider, say, an inferior television costing $200 and a superior television costing $800 unethical.
No, you don't. The difference is one of transparency. Information about various televisions and their pricing is freely available to anyone who asks, whereas reliable information about the necessity or possibility of bribes is hard to obtain. The end result is a less efficient market.
And a less efficient market is necessarily unethical? I also don't think the situation is opaque: tip well, be genuinely friendly, and you'll receive better service.
People will find a market unethical if it's consistently biased in a way that seems unnecessary and "unfair." In this context, since bribery isn't a common part of American culture, it seems unfair to give an advantage to people who are skilled at it.
The situation you described is very opaque, compared to the television market. How well is "well," and how much better might the service be? The answers vary wildly depending on your manner and the establishment in question, and you're almost never going to know them before you pay.